The Internet has changed society and is as much a part of modern culture as television and telephones. People are becoming increasingly connected to share and access information. This interconnectivity promotes improvements in the computing and communication infrastructure.
Much of this infrastructure was designed for entertainment or communication, but is being adapted to deliver general data. The addition of general information and data transmission over the legacy infrastructure has necessarily been somewhat restrained by the need for the infrastructure to continue its initial functions. Furthermore, legacy technical characteristics of this infrastructure influence the various solutions to include information storage and transmission. Most major entertainment and communication channels now include computer networking capabilities.
Many people get their television service through cable television (CATV). CATV was initially developed to deliver television signals to areas where antennas had difficulty picking up television broadcasts. Coaxial cabling is the primary type of cabling used by the cable television industry because it is much less susceptible to interference and can carry large amounts of data.
Television signals are broadcast in 6 MHz channels and this channel bandwidth was incorporated into cable television. As transmission demands increased, parts of the coaxial backbone were replaced with optical fiber to create a hybrid fiber-coaxial (HFC) network. The bandwidth of the cable infrastructure makes it an attractive technology to incorporate data transmission.
An example use of data over a cable television network was approved by the International Telecommunications Union (ITU) which includes interface requirements for high speed data communication, and is called the data over cable service interface specification (DOCSIS).
Cable service providers also offer internet service through the cable television network in 6 MHz channels for downstream data. Upstream data has historically received less bandwidth and has been offered in a fraction of a channel, such as in 2 MHz provisions. This asymmetry was due to the Internet initially being an information provider. Currently, peer-to-peer computing, file sharing, gaming, and other uses have increased the need for upstream bandwidth.
Due to the legacy CATV infrastructure primarily being a broadcast channel, there are different modulation schemes for upstream and downstream transmission, for example, downstream utilize 64 and 256 Quadrature Amplitude Modulation (QAM) and upstream utilizes Quadrature Phase Shift Keying or 16 QAM.
Furthermore, to allow maximum data transmission through different networks, DOCSIS supports use of various combinations of modulation and therefore different data rates, which in turn complicates the physical layer in these networks.
Placing upstream and downstream data onto the cable television network requires special equipment at each end of the HFC plant. On the customer end, a cable modulator/demodulator (cable modem, or CM) transmits and receives data over the cable television infrastructure and on the cable provider end a cable modem termination system (CMTS) is used to place and retrieve data from the cable television network.
Typically a CMTS broadcasts to numerous CMs over a shared channel while each CM separately sends upstream data. In this framework, a cable modem must select only the broadcast downstream data that is intended for it while it must follow an arbitration protocol to avoid data collisions with other cable modems while transmitting upstream data.
Cable modems are identified by Service Identifiers (SIDs). SIDs are used as a BPI (baseline privacy) index on the downstream (DS) and also to designate upstream data to certain CMs for the CMTS on the upstream (US).
The upstream bandwidth is allocated by a CMTS and is shared among multiple CMs. Upstream transmissions are divided into mini-slots which may carry up to 1024 bytes, but in practice often contain considerably less bytes to conserve bandwidth. The arbitration protocol for upstream transmissions is assigned by a CMTS in response to requests by CMs. The CMTS communicates these assignments to each cable modem with a media access control (MAC) packet called a mini-slot allocation packet (MAP).
Currently, upstream bandwidth is limited. What is needed is a method and apparatus to satisfy the requirements of peer-to-peer computing, file sharing, distributed computing, gaming, and other applications which have an increased need for upstream bandwidth.